This invention relates to a plate evaporator or plate condenser which comprises a plurality of substantially rectangular plates stamped and profiled from sheet metal. The plates are guided in alignment with one another in a machine stand between an end plate affixed to the machine frame and a head plate movable with respect to the machine frame. The plates are, during operation, pressed to one another to form a plate stack. In this state, adjoining plates alternatingly define among themselves--with the aid of circumferential seals disposed in corresponding grooves of the plates--flow chambers for a fluid to be evaporated, on the one hand and for a fluid to be condensed, on the other hand. The two fluids are guided parallel to one another. The flow chambers are supplied with the fluid to be evaporated and with the fluid to be condensed, by means of aligned inflow and outflow openings formed by apertures in the plates, together with associated circumferential seals. The plates are, by means of their profiles, in mutually supporting contact with one another at locations on the plate faces.
In evaporators or condensers of the above-outlined type the fluid to be condensed is, as a rule, passed from above downwardly, while the fluid to be evaporated is, as a rule, guided in a counter current. The known plates have apertures for the inflow and the outflow for the fluid to be evaporated, on the one hand and for the fluid to be condensed, on the other hand. As a rule, these apertures are arranged in the corner zones of the rectangular plates or partly across their width in the upper or lower margin thereof. This means that the fluids first have to spread from the apertures over the chamber formed between the plates and then they have to be eventually again collected into a predetermined flow direction. This circumstance alone leads to an irregular or non-uniform stressing of the plate surfaces by the fluids and to the formation of non-uniform or partially interrupted liquid films.
Further, the plates are, over all the chambers, supported on one another by embossments such as cams or spherical protrusions and also partially by bead-like embossments guiding the fluid. This leads, particularly on the evaporator side, to permanent interruptions and disturbances in the liquid film under formation and thus results in undesirable turbulences.
In case the fluid to be evaporated contains solid particles, the above-outlined arrangements do not allow a dissipation of large, heat-caused stresses and further, the evaporation chambers are likely to be clogged by the solid particles. In this respect particularly the flat regions of the plates cause problems which, because of the flow conditions, are non-uniformly or alternatingly stressed by the fluid, so that in those locations overheating may occur which leads to a baking of the solids to the plate wall. Further, the continuous interference with the liquid film by the supporting cams and spherical embossments between the plates tend to prevent, on the one hand, a uniform heat exchange and, on the other hand, tend to create zones in which the above-noted phenomena of overheating may occur, together with the described consequences. For example, in an evaporator, high-viscosity concentrates may remain suspended at the cams or spherical embossments, as a result of which, during operation, the flow passage cross sections may change or be influenced additionally so that a relatively frequent opening and cleaning of the plates is necessary.
It is a further disadvantage of the known plate evaporators or condensers that the heat contained in the condensate cannot be utilized efficiently. In the known arrangements the heat is either dissipated without utilization or the condensate is used for prewarming the fluid to be evaporated, with the aid of an additionally required pump and an additionally required heat exchanger.